Limestone

As limestone sedimentary rocks are referred to the (CaCO3) Calcite and aragonite consist overwhelmingly of the chemical substance calcium carbonate in the form of minerals.

Limestone is an extremely variable rock; which affects both its formation and its properties, the appearance and economic availability. There is, therefore, within the geology own field of study, the carbonate sedimentology, which deals exclusively with the formation and the properties of the different limestone types. The majority of the limestones is of biogenic origin ( deposited by living things ), but there are also chemically precipitated and clastic limestones.

Limestones have enormous economic importance as a raw material for the construction industry and as natural stone. Furthermore, such deposits reservoir rock for oil and gas.

• 7.1 General
• 7.2 Europe
• 7.3 Special forms of limestone

Disambiguation

The term limestone is used both in the vernacular as well as in the technical and scientific jargon different. While the term rather broadly used in the scientific language and besides the strong solidified limestone also relatively brittle rocks such as chalk impute the limestones, the term used in the building materials industry is rather limited on highly consolidated limestones.

We use the word in the natural stone industry polishable limestone often called " marble ", although they are no marbles in the geological sense. Marble is a metamorphic rock in the earth sciences.

Composition

Limestone consists predominantly of the minerals calcite and aragonite, two forms of crystallization of calcium carbonate ( calcium carbonate CaCO3). In more or less varying proportions of other minerals are found. These include clay minerals, dolomite ( CaMg ( CO3) 2 ), quartz, gypsum and others. Outweighs the dolomite proportion, one speaks of the rock dolomite. Does the limestone a relatively high proportion of clay minerals, we then referred to him as marl. Limestone may also contain up to several percent of organic matter, and is then called bituminous lime ( in the presence of hydrogen sulfide and Stinkkalk ).

Formation of limestone

Limestones may belong within the sedimentary rocks of several types. However, the majority of the limestones is of biogenic origin, meaning it was formed and deposited by living things. Limestone can also be by chemical processes (which in turn may be influenced by living organisms ) are precipitated from the water. Furthermore, a rock which is composed of calcium carbonate (limestone or marble), eroded, transported and elsewhere as clastic sediment can be deposited again.

Biogenic limestone

In biogenic origin limestone is mostly deposited microorganisms or rock-forming corals. Subordinate one also finds limestones that consist predominantly of snails, clams or sponges. In any case, the rock consisting of calcium carbonate, which was part of the creatures and was deposited for the construction of external or internal skeletons.

Deposited by micro- limestone

From microorganisms deposited limestones - the chalk is one of them - are usually fine, microcrystalline sedimentary rocks, which are created by deposition of shells of fossil micro-organisms, especially coccoliths of coccolithophores and foraminifera shells of. Also kalkabscheidende algae and bacteria ( stromatolites ) can be rock-forming. Due to their often massive structure, they are also referred to as Massenkalke. It is found in rocks but also precipitated calcite, so that smooth transitions to the precipitated limestone exist. More or less frequent and often tied to very limited locations can be found with the naked eye visible macrofossils, which thus show transitional stages to the Fossilkalken.

The rock is formed when fall after the death of living creatures, the shells on the ground and first form so-called lime sludge. However, lime sludge can form only up to a certain depth in the open ocean. Below the so-called Carbonatkompensationslinie the calcium carbonate is fully dissolved due to the water pressure so that the sediment below the line are always carbonate. The depth of the Carbonatkompensationslinie varies; it is for example in the tropics 4500-5000 meters water depth.

Due to the diagenesis of sludge then arises solid limestone. During the solidification of new calcite crystals form. Here, most of the originally existing aragonite to calcite is converted. So cavities with later ( secondary) formed crystals can be filled or the existing sedimentary structures are more or less completely obliterated by strong recrystallization.

Fossilkalke

As Fossilkalke refers to rocks or layers within otherwise massive limestones, consisting for the most part from the visible to the naked eye fossils. Worldwide the most common are Korallenkalke as significant rock thicknesses may be caused by growth of coral reefs. Other, often found Fossilkalke one named after her ( the principal ) rock formers Molluskenkalk, foraminous (also nummulite ) Brachiopodenkalk, Bryozoan, Goniatitenkalk, Crinoidenkalk or for other animal groups. Nulliporenkalk created by kalkabscheidende, multicellular algae. Rock made ​​of shells are referred to as limestone or if the structure is very clearly visible, as a clam Schill.

The fossils preserved in limestone, a distinction between communities and grave communities. Communities represent the occurring on the spot organisms and can be embedded directly after her death in the sediment or soil-dwelling creatures as are already embedded. Grave communities are transported by currents and other transport mechanisms and redeposited at a suitable location ( eg current shadow ). The living entities contained therein have mostly not inhabited a habitat.

While corals and other reef limestones form as already quite solid limestone, the other Fossilkalke first pass through a diagenetic hardening similar to those discussed above Massenkalken. By subsequent recrystallizations all Fossilkalke, the reef limestones can change significantly.

Chemical and biogenic precipitated limestone

Naturally occurring water (both marine and freshwater ) always contains more or less large amounts of calcium carbonate, usually it is solved as calcium bicarbonate, because its solubility is significantly larger than that of the carbonate ion. If carbonate fed to saturation of the solution or decreases conversely of solubility of the water, so calcium carbonate is precipitated from the supersaturated solution. This was previously not part of living organisms. This limestone may be part of Evaporitserien. Eindampfungsfolge occurs within the limestone due to the relatively low solubility of the carbonate at the base of the rock range. He is first deposited. In the hanging wall is usually followed by gypsum and above the slightly soluble salt rocks, for example rock salt. In the sea calcite crystals can be deposited only in the uppermost 200 m, because at greater depths by increasing water pressure, the solubility of carbon dioxide increases and therefore occur no more supersaturated solutions. The precipitated crystals can but fall to Carbonatkompensationslinie.

The precipitation of calcium carbonate can run completely without the participation of living organisms, but is mostly supported by the activity of living organisms (especially algae in freshwater and mosses). The plant photosynthesis consumes carbon dioxide in the water, so that split again into carbon dioxide and carbonate ions to maintain the solution equilibrium hydrogen carbonate ions. As carbonate ions are much less soluble than bicarbonate ions, calcite is now increasingly precipitated from the solution.

The precipitation of calcite occurs both within the water column and at the bottom of bodies of water directly on the ground. In the first case form in the water body microscopic crystals that fall to the ground and also make lime sludge there. Your diagenesis leads to a solid limestone. In the second case, the calcite crystals grow directly on other crystals on the body of water, so that they can also settle in streams. This mechanism is needed for the formation of travertine.

Clastic limestones

Clastic sedimentary rocks may, under certain conditions, almost entirely composed of calcium carbonate and are then usually referred to as limestone. Strictly speaking, they should be placed in one of the categories of clastic sediments. Usually, these sediments have a large grain size, since smaller particles carbonate is quickly destroyed. Similarly, the grains were mostly transported over short distances due to the low mechanical and chemical resistiveness. The most common are called Riffhangbrekzien, which accumulates at the base of a coral reef broken off, usually square Riffmaterial. Petro Graphically, these are more of a breccia as a limestone. A special case is the calcarenite in which fossil fragments are mixed with fragments of other limestones, which originated in marine shallow water zones. In some cases an even more fine-grained micritic mass binds the small clasts.

Classification of clastic limestones ( according to the average grain size ):

• Rudit > 2 mm
• Arenite 2 to 0.063 mm
• Siltit 0.063 to 0.004 mm
• Lutit 0.004 to 0.001 mm
• Kryptit < 0.001 mm

Appearance

Limestones have in most cases a bright, gray to gray- yellow color. By admixtures of other minerals (eg iron compounds ) are also stronger, especially red colors are quite common. Bituminous limestones can also be dark gray to black. Chemically precipitated limestones or limestones deposited microorganisms are fine-grained and dense usually. Depending on the conditions of origin one finds more or less frequently fossils. Fossilkalke other hand, have many easily recognizable fossils. These limestones often contain pores and other cavities. Extremely large cavities contain Süßwasserkalke, especially travertine.

Weathering of the limestone karst and Süßwasserkalke

Because of the relatively high solubility of the carbonate limestone is preferred over chemical weathering relatively susceptible rocks, and therefore, forms a special solution forms from. Conversely, however, the dissolved carbonate are precipitated again and also special rocks and shapes ( tufa, travertine, travertine ) produce. Both are collectively referred karst or karst.

On the weathering of exposed limestone is a characteristic soil type is emerging that rendzina. Weathered limestone underground, caves occur. In the interplay of various factors, caves form as the Erdmannshöhle in hazel. The stalactites in these caves grow as travertine.

Economic use

Depending on their properties, are limestones extremely versatile. Especially dense limestones can be used as easy to work with natural stones.

For the construction industry limestone is one of the most important raw materials. For this, he is treated in lime plants and converted into quicklime. Or it is baked ground and mixed with clayey materials to cement, which represents the binder for the production of concrete (mixture of cement, water and aggregates such as sand and gravel). Limestone is also used in the glass industry, as it brings calcium into the molten glass.

When carbonate is limestone flue gas desulfurization. Finely ground limestone is used in the agriculture and water against the acidification of soil and water. The calcium compound is used as a supplement in the glass industry and for slag formation in the cottage industries. On the basis of this composition, limestone is used as a fertilizer.

Very pure limestones ( white lime ) are raw materials for the chemical industry or to Terrazzo further processed (Ulmer white lime ).

Porous limestones, especially the Fossilkalke, are one of the most important reservoir rocks for oil and gas. The richest oil deposits in the earth on the Arabian Peninsula are reef limestones that have arisen in the Jurassic and the Cretaceous. Therefore limestone serves as an indicator for the prospecting of deposits.

Limestone lower quality, that have been usually considered a waste product, to be used increasingly in recent years for the production of hard paper.

Occurrence

Generally

Limestones are on the continents and Schelfen very widespread rocks. They are found both on relatively old geological plates as well as in geologically young mountains. However, within the very old shields and the deep ocean basins they come back. The vast majority of limestones was originally formed in the sea ( flat) and lifted by tectonic processes above sea level. Terrestrial ( formed on the mainland) limestones almost always require older limestone deposits in the vicinity which are necessary as a delivery area of the calcium. For example, the Travertinvorkommen in Thuringia are always linked to the presence of limestones from the Muschelkalk.

Europe

Large limestone deposits are located in Central Europe in the central and southern part of Germany (mainly using limestone from the limestone and the upper Jurassic), in the Swiss and French Jura Mountains and in the northern and southern Alps. Furthermore limestones are found very often referred to as glacial boulders in northern Germany. The limestone boulder mostly hail from southern and central Sweden, and from the middle and northern Baltic Sea basin.

Great landscapes, which are overwhelmingly dominated by limestone, are, for example, the Swabian and the Franconian Jura and the northern Limestone Alps or the coast of Dalmatia. The best known in Germany mining area is located in the Altmühtal the Solnhofen limestone and Jurassic limestone.

Significant Travertinvorkommen are located in Germany, for example, in Stuttgart-Bad Cannstatt and in the Thuringian basin (eg Weimar- Ehringsdorf ).

Chalk is revealed at numerous locations along the European chalk belt. The belt extends from the UK via France to the middle Baltic Sea and is also mined in places.

At least since the ancient Roman limestone is mined, for example, on the island of Brač (building material Diocletian's Palace in Split ). At one of the oldest mining sites for limestone in Germany include the historic limestone quarry Ruedersdorf in Brandenburg, which goes back to the work of the Cistercians in the 13th century.

Special forms of the limestone

Special varieties:

• Faxekalk
• Calcarenite

Süßwasserkalke:

• Stalactite
• Stone trough
• Moonmilk
• Limestone sinter terraces of Pamukkale, Mammoth Hot Springs and in Plitvice Lakes National Park

Types of natural stone

• Adnet Limestone ( Austria )
• Kaiserstein
• Jurassic limestone ( Bavaria )
• Solnhofen ( Bavaria )
• Elmkalkstein (Lower Saxony)
• Cannstatt Travertine (Baden- Württemberg)
• Blue stone (natural stone ) ( Nordrhein-Westfalen)
• Belgian granite or granite Petit (Belgium )
• Irish Limestone (Ireland )
• Marès (Mallorca)
• Meleke (Israel )
• Savonnières (France)
• Urgonian (France)